2,3,3,3-Tetrafluoropropene (CF3CF═CH2) (hereinafter sometimes referred to as “HFO-1234yf), which contains no chlorine, is useful as an alternative to Freon such as a chlorofluorocarbon to be used as a refrigerant, etc.
As a method for producing HFO-1234yf, a method may be mentioned in which 1,1-dichloro-2,2,3,3,3-pentafluoropropane (CF3CF2CHCl2) (hereinafter sometimes referred to as “HCFC-225ca”) is subjected to dehydrofluorination to obtain 1,1-dichloro-2,3,3,3-tetrafluoropropene (CF3CF═CCl2) (hereinafter sometimes referred to as “CFO-1214ya”), and the obtained CFO-1214ya is reduced by reaction with hydrogen to obtain HFO-1234yf.
As a method of reducing CFO-1214ya to obtain HFO-1234yf, for example, the following method (i) disclosed in Patent Document 1 may be mentioned. (i) A method of subjecting CFO-1214ya and a hydrogen gas to a reaction represented by the following formula (6) in the presence of a palladium catalyst supported on alumina, at from 100 to 400° C., preferably from 125 to 350° C.:CF3CF═CCl2+2H2→CF3CF═CH2+2HCl  (6)
However, by the reaction represented by the above formula (6), 1,1,1,2-tetrafluoropropane (CF3CHFCH3) (hereinafter sometimes referred to as “HFC-254eb”) and 3,3,3-trifluoropropene (CF3CH═CH2) (hereinafter sometimes referred to as “HFO-1243zf”) which are over-reduced products form as by-products.
If over-reduced products form in a large amount, the yield of the aimed product decreases, and the production efficiency decreases. Further, HFO-1243zf has a boiling point close to that of the aimed HFO-1234yf, and is thereby hardly separated and removed by subsequent distillation. Accordingly, HFO-1243zf will remain as an impurity in HFO-1234yf obtainable by distillation, and a separation and purification step is additionally required to obtain a high purity product.
Further, Patent Document 2 discloses the following method (ii) as a method of carrying out a reduction reaction similarly. (ii) A method of reacting RfCF═CX2 (wherein Rf is a C1-10 fluoroalkyl group, and X is chlorine, bromine or iodine) with hydrogen at from 5 to 200° C. in the presence of a palladium catalyst supported on activated carbon to obtain RfCF═CH2.
However, in the method (ii) also, RfCH═CH2 which is an over-reduced product forms as a by-product together with the aimed RfCF═CH2. For example, in a case where Rf is CF3—, that is, in a case where the aimed product is HFO-1234yf, the over-reduced product is hardly separated from the aimed product by distillation in the same manner as the method (i).
Further, as a method for reducing chlorine in a chlorofluoroolefin, Patent Document 3 discloses the following method (iii). (iii) A method of subjecting chlorotrifluoroethylene and a hydrogen gas to a reaction represented by the following formula (9) in the presence of a palladium catalyst supported on activated carbon at from 100 to 350° C., preferably from 200 to 250° C.:CF2═CClF+H2→CF2═CHF+HCl  (9)
Further, Patent Document 4 discloses the following method (iv).
(iv) A method of subjecting 1,2-dichlorodifluoroethylene and a hydrogen gas to a reaction represented by the following formula (10) in the presence of a palladium catalyst supported on activated carbon at from 150 to 600° C., preferably from 200 to 400° C.:CClF═CClF+2H2→CHF═CHF+2HCl  (10)
However, in the methods (iii) and (iv) also, in addition to the aimed product, an over-reduced product will form as a by-product, whereby the impurity of the aimed product will decrease.